Field of the Invention
The present invention relates to a printing apparatus and a driving method therefor.
Description of the Related Art
A printing apparatus includes, for example, a printhead for printing dots on a printing medium, and a conveying roller for conveying the printing medium. For example, in an arrangement in which printing is executed on a printing medium such as a longitudinally long-shaped sheet (roll sheet) while conveying the printing medium, the frictional force between the conveying roller and the printing medium can change due to a change in environment such as heat and humidity. Therefore, the conveying speed of the printing medium may change while printing is executed by conveying the printing medium. This may cause a print position shift by the printhead, thereby degrading the image quality.
Japanese Patent Laid-Open No. 2005-138374 exemplifies a method of correcting the timing of printing of dots in accordance with a change in conveying speed. An example of a method of correcting the timing of printing of dots is a method of delaying printing timings by some nozzle arrays by inserting null data to print data, and synchronizing the printing timings with those by the remaining nozzle arrays. This method is advantageous in improving the image quality since a print position shift caused by a change in conveying speed is corrected.
In some printing apparatuses, a printhead includes two or more nozzle arrays which are used to print dots of the same color and each of which has a plurality of nozzles arranged along a predetermined direction. Print data are distributed to the respective nozzle arrays, and the respective nozzle arrays are simultaneously driven based on the distributed print data. This arrangement is advantageous in improving the print speed since the two or more nozzle arrays are driven in parallel to print dots according to the print data.
Japanese Patent Laid-Open No. 2012-30594 (e.g. FIG. 8C) discloses a technique in which the nozzles of each group of two nozzle arrays are time-divisionally driven, and each nozzle array is time-divisionally driven by shifting the driving timings by a ½ period of time-divisional driving. Similarly, Japanese Patent Laid-Open No. 2012-30594 (e.g. FIG. 11C) discloses a technique in which the nozzles of each group of four nozzle arrays are time-divisionally driven, and each nozzle array is time-divisionally driven by shifting the driving timings by a ¼ period of time-divisional driving.
In the arrangement described in Japanese Patent Laid-Open No. 2012-30594, however, when the conveying speed of a printing medium is increased to improve the throughput, it is necessary to increase the operation speed of each nozzle array (for example, the driving frequency of each nozzle array) so that dots are appropriately printed on the printing medium at a speed corresponding to the conveying speed. This requires the user to change the design of hardware such as the circuit design of a printing apparatus along with a change in operation speed, leading to an increase in manufacturing cost.